D & H,
The Ford 7.3 International Harvester Diesel engine from 1999 to 2003 is a great engine, arguably the best, most reliable Ford has ever used. Also the drivetrain, like the Sterling axle is good as gold. My bro has the '99 with a lot of hard miles towing and it has been bullet-proof. His mileage is about the same as yours. The one thing he has that you don't, which may affect outcome is he has the German, aluminum case, ZF-6 speed manual trannie.
You are just a victim of bad luck and inattention.
I would not give up on it so soon. What I would do is find a good, non-Ford dealer diesel mechanic. I bought my '01.5 Dodge CTD/NV5600 brand new and used the factory people until the warranties expired. I cannot remember anything going wrong during the warranty period, of course. Subsequently, it was only great aftermarket diesel mechanics. Fortunately, I've had very little trouble with it but still have my go-to guru diesel guy on my speed dial...just in case, you know,....just in case. Also fortunate for me is our now 7 yr. home base on the West Slope is Dodge Diesel country with Dodge far outweighing Ford and GM on light trucks. So, we have a plethora of mechanics who know their business well.
Now, a bunch of niggling little woes are starting to appear, like plastic brackets and parts that go south, like the e-brake release paddle which broke 10 days ago. Original everything except:
Aftermarket air cleaner, on the second aftermarket lift pump, changed the trans oil once, batteries, brakes twice, tires and wheels, bigger shocks, a new fan belt, and added some secondary springs and a steering box/frame brace, new longer four links in front and a 3" lift,...that's about it. No clutch, trans, t-case, axle bearings, RG&P's, radiator.
As far as fit and finish, Ford is still on top in my book with Dodge at the bottom of the list and GM, ho-hum in the middle. Just my observation.
Anyway, don't give up just because bad luck has followed you around of late.
Remember my admonition:
"Most of the woes of the world can be directly attributed to someone not paying attention."
It seems someone is finally paying attention.
regards, as always, jefe